Merge branch 'main' into scroll-markers

Author: flackr

css-align-3/Overview.bs

@@ -771,7 +771,9 @@ Distributed Alignment: the ''<content-distribution>/stretch'', ''space-between''
 
 	These values are represented with the <<content-distribution>> grammar term:
 
-	<pre class='prod'><dfn>&lt;content-distribution></dfn> = space-between | space-around | space-evenly | stretch</pre>
+	<pre class='prod'>
+	<dfn>&lt;content-distribution></dfn> = space-between | space-around | space-evenly | stretch
+	</pre>
 
 <h3 id='overflow-values'>
 Overflow Alignment: the ''safe'' and ''unsafe'' keywords and scroll safety limits</h3>
@@ -865,31 +867,86 @@ Overflow Alignment: the ''safe'' and ''unsafe'' keywords and scroll safety limit
 		<dt>(no value specified)
 		<dd>
 			If the <a>overflow alignment</a> isn't explicitly specified,
-			the default <a>overflow alignment</a> is a blend of “safe” and “unsafe”
-			in that an overflowing <a>alignment subject</a> is allowed to overflow its <a>alignment container</a>,
-			but if this would cause it to also overflow
-			the <a>scrollable overflow area</a> of its nearest ancestor <a>scroll container</a>
-			(thus extending into the “unscrollable” region),
-			then its overflow in that direction is limited
-			by biasing any remaining overflow to the opposite side.
-
-			Issue: It may not be Web-compatible to implement the “smart” default behavior
-			(though we hope so, and believe it to be likely),
-			so UAs should pass any feedback on this point to the WG.
-			UAs that have not implemented the “smart” default behavior
-			must behave as ''safe'' for 'align-content' on [=block containers=]
-			and ''unsafe'' otherwise.
+			the default <a>overflow alignment</a> is a blend of “safe” and “unsafe”.
+			See [[#auto-safety]] for details.
 	</dl>
 
 
-<!--
-                   ██████   ███████  ██    ██ ████████ ████████ ██    ██ ████████
- ██   ██          ██    ██ ██     ██ ███   ██    ██    ██       ███   ██    ██
-  ██ ██           ██       ██     ██ ████  ██    ██    ██       ████  ██    ██
-█████████ ███████ ██       ██     ██ ██ ██ ██    ██    ██████   ██ ██ ██    ██
-  ██ ██           ██       ██     ██ ██  ████    ██    ██       ██  ████    ██
- ██   ██          ██    ██ ██     ██ ██   ███    ██    ██       ██   ███    ██
-                   ██████   ███████  ██    ██    ██    ████████ ██    ██    ██
+<h4 id=auto-safety>
+Automatic Overflow Alignment Safety</h4>
+
+	If no [=overflow alignment=] mode is specified for a property,
+	the default behavior lies somewhere between ''safe'' and ''unsafe'',
+	and also varies by layout mode.
+
+<h5 id=auto-safety-scroll>
+Content Distribution for Scroll Containers</h5>
+
+	The default [=overflow alignment=] behavior
+	for [=content distribution=] on [=scroll containers=] is ''unsafe''.
+	Non-''normal'' values of the [=content distribution properties=] instead
+	alter the [=scrollable overflow area=] in order to allow access to the overflowing content.
+	See [[#overflow-scroll-position]].
+
+<h5 id=auto-safety-position>
+Self-Alignment for Absolutely Positioned Boxes</h5>
+
+	For [=absolutely positioned=] [=alignment subjects=] whose
+
+	* relevant [=self-alignment property=] is not ''justify-self/normal'' and
+	* whose 'inset-area' property successfully defines an [=inset-area grid=]
+
+	the default [=overflow alignment=] behavior is as follows:
+
+	1. If the [=alignment subject=] overflows its [=inset-modified containing block=]
+		(its normal [=alignment container=]),
+		but does not overflow its [=original containing block=]
+		align as specified (''unsafe'').
+	2. If the <em>size</em> of the [=alignment subject=]
+		fits within its [=original containing block=],
+		but its specified alignment would cause it to overflow the [=original containing block=],
+		it is instead shifted the minimum amount
+		to stay within the [=original containing block=]
+		while honoring the alignment as much as possible
+		(i.e., flush with the edge of the [=original containing block=]
+		it was trying to overflow over).
+	3. If the size of the [=alignment subject=]
+		overflows the [=original containing block=],
+		it is instead start-aligned within the [=original containing block=]
+		(similar to ''safe'').
+
+	(For [=absolutely-positioned=] [=alignment subjects=] that fail the above conditions,
+	see [[#auto-safety-defaults]].)
+
+<h5 id=auto-safety-default>
+All Other Alignment</h5>
+
+	For all other elements:
+
+	1. If the [=alignment subject=] overflows its [=alignment container=],
+		align as specified (''unsafe'').
+	2. If the [=alignment subject=] would overflow
+		the [=scrollable overflow area=] of its nearest ancestor [=scroll container=],
+		(thus extending into the “unscrollable” region),
+		then its overflow in that direction is limited
+		by biasing any remaining overflow to the opposite side.
+
+	Issue: It may not be Web-compatible to implement the “smart” default behavior
+	(though we hope so, and believe it to be likely),
+	so UAs should pass any feedback on this point to the WG.
+	UAs that have not implemented the “smart” default behavior
+	must behave as ''safe'' for 'align-content' on [=block containers=]
+	and ''unsafe'' otherwise.
+
+<!-- Big Text: *-content
+
+               ███▌   ███▌  █    █▌ █████▌ █████▌ █    █▌ █████▌
+ █   █        █▌  █▌ █▌  █▌ █▌   █▌   █▌   █▌     █▌   █▌   █▌
+  █ █         █▌     █▌  █▌ ██▌  █▌   █▌   █▌     ██▌  █▌   █▌
+███████ ████▌ █▌     █▌  █▌ █▌▐█ █▌   █▌   ████   █▌▐█ █▌   █▌
+  █ █         █▌     █▌  █▌ █▌  ██▌   █▌   █▌     █▌  ██▌   █▌
+ █   █        █▌  █▌ █▌  █▌ █▌   █▌   █▌   █▌     █▌   █▌   █▌
+               ███▌   ███▌  █▌   ▐▌   █▌   █████▌ █▌   ▐▌   █▌
 -->
 
 <h2 id='content-distribution'>